7117

• UCREFRP Catalog Number: 7117
• Author: Barrett, J. C. and G. D. Grossman
• Title: Effects of Direct Current Electrofishing on the Mottled Sculpin
• USFW Year: 1988
• USFW - Doc Type: North American Journal of Fisheries Management
• Copyright Material: YES

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BARRETT AND GROSSMAN

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Days after capture

FIGURE I.-Survival of mottled sculpin after capture
by clectro6.iling (treatment) or kick-seining (control) in
experiment I (A) and II (B), Numbers adjacent to lines
represent tank numbers,

12 to 14'C. Both groups offish were weighed and
measured, marked with subcutaneous injections
of acrylic paint, and randomly released into one
of the four sections (two treatment sections and
. two ,control sections), These fish ranged from 38
to 79 mm SL (mean :t SD, 55.4 :t 8.5 mm) and
from 1 to 12 g in weight (3.88 :t 1.92 g). All the
stream sections initially contained 25 mottled
sculpin. Each week, fora total of 4 weeks, we
electrofished the two treatment sections for 30 s
with nonpulsed DC at 600 V (200 W continuous
output), All fish were then collected with hand nets
and checked fortheir acrylic paint marks. At weeks
0, 3, and 4, we also weighed and measured these
fish. Control fish were treated identically except
that the electrodes of the electroshocker were not
eneJgized as they passed through the control stream
sections. We removed dead fish and calculated
survival times as in experiments I and II.
Totest the hypothesis that electrofishing had no
effect on survival, a Kruskal-Wallis test was used
to check for significant differences in the survival
time of fish in each section. As in the tank exper-
iments, we also tested for treatment effects by
pooling the data for each treatment (i.e., both con-

trol sections versus both treatment sections) and
testing for a significant difference using a Mann-
Whitney test.

Results

Tank Experiments

In experiment I, overall survival of mottled
sculpin in each of the tanks exceeded 88% in all
cases (Figure IA). Mottled sculpin survival in the
treatment tanks (mean, 99%) exceeded survival in
the control tanks (mean, 94%). There were no sig-
nificant differences in survival times offish among
tanks (Kruskal-Wallis test; P > 0.10). Similarly,
we also failed to detect a significant difference be-
tween pooled survival times of fish in treatment
and control tanks (Mann-Whitney test; P > 0.10).
Thus, mottled sculpin survival in experiment I
was not significantly affected by either tank or
treatment effects.
In experiment II, overall survival of mottled
sculpin in each of the tanks exceeded 85% in all
cases (Figure I B), Survival in the treatment tanks
(mean, 95%) slightly exceeded survival in the con-
trol tanks (mean, 93%). We could not detect sig-
nificant differences in the survival times of fish in
each tank (Kruskal-Wallis test; P > 0.10). We then
tested pooled data for treatment and control tanks
and found no significant differences (Mann-Whit-
ney test; P > 0,10), suggesting that neither tank
nor treatment effects were present in this experi-
ment.
Survival times for other species were recorded,
but sample sizes were too low to permit statistical
testing of these results, Mortality patterns for these
species, however, were similar to the patterns ob-
served for mottled sculpin, with little or no mor-
tality during the first 30 d after capture.

Henson Creek Experiment

All fish survived the first 7 d of the experiment.
After handling or handling plus electroshocking
on days 7, 14, and 21, survival declined in all
sections (Figure 2). There were no significant dif-
ferences in survival of fish from the four stream
sections (Kruskal-Wallis test; P > 0.05). We also
failed to detect a significant difference between the
pooled treatment data (sections 2 and 3) and the
pooled control data (sections I and 4; Mann-
Whitney test; P > 0, I 0), Hence, we were unable
to demonstrate either a section or treatment effect
in this experiment, suggesting that repeated han-
dling rather than e]ectroshocking was responsible
for the observed mortality.

EfFECTS OF ELECTROFlSHING ON SCULPIN

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Days after capture

FIGURE 2,-Survival of mottled sculpin subjected to
repeated electroshocking and handling (treatment) or just
handling (control) in four artificial stream sections at
Henson Creek. Black arrows indicate the time of han-
dling and electroshocking episodes. Numbers adjacent
to lines represent section numbers.

Discussion

Our experiments indicate that electrofishing did
not have a significant effect on mottled sculpin
survival (over a 30-d period), regardless ofwheth-
er the fish experienced either single or multiple
exposures to electricity. No mottled sculpin died
within 7 d of capture in any of the treatments, and
mortalities among fish subjected to a single elec-
trofishing exposure did not begin until 17 dafter
capture. These results suggest that fish were not
acutely injured during collection as has been re-
ported previously for e]ectroshocked fish (Hauck
]949; Spencer 1967; Hudy 1985). The overall
mortality among our once-exposed mottled scul-
pin (0-10.5%) was less than that observed in other
investigations (Hauck 1949; Horak and Klein 1967;
Spencer 1967) and may be due to our use of direct
current electricity, which is less harmful than al-
ternating current (Pratt 1954; Spencer 1967).
If electrofishing does have a de]eteriouseffect
on mottled sculpin, that effect should have been
most obvious in our Henson Creek experiment
wher~ treatment fish were repeatedly exposed to
electricity over a relatively short time period. Our
failure to detect significant differences in the sur-
vival of electroshocked and control fish at Henson
Creek strongly suggests that exposure to electricity
alone does not result in appreciable mortality in
mottled sculpin. Overall survival at Henson Creek,
however, where fish were handled repeatedly, was
much lower than that observed in our tank ex-
periments, where fish were handled only once. Be-

cause a significant electrofishing effect was not de-
tectable in the Henson Creek data, this suggests
that handling stress has a greater effect on mottled
sculpin survival than does electrofishing. We can-
not explain why most mortality at Henson Creek
occurred after the second handling and electro-
shocking exposure (on day 7).
The Henson Creek experiment had several ad-
vantages over the tank experiments, including re-
peated exposure to electricity over a short time
period, reduced disease problems, the presence of
natural prey, and a more natura] habitat. Conse-
quently, we suggest that future studies on stream
fishes be done in experimental stream channels
rather than in tanks or simulated streams.
There is evidence that exposure to electrofishing
produces sublethal physiological changes in fishes,
specifically increases in blood lactate and creatine
phosphokinase levels (Schreck et a!. 1976; Bouck
et a!. ] 978; Bums and Lantz 1978). Ifsuch changes
occurred in our electroshockedfish, the\'c:ilppar-
ently did not differentially affect survival.(B~cause
even mild handling can produce physiological im-
balances in fishes (Wedemeyer 1972; Pickering et
a!. 1982), it may be that control fish in our ex-
periments suffered as much physiological distress
as treatment fish. Nonetheless, the lack of a sig-
nificant treatment effect indicates that any phys-
iological changes produced by electrofishing did
not significantly affect mottled sculpin survival.
One difficulty in comparing our results to those
from earlier studies is the general lack of meth-
odological uniformity among studies, represented
by differences in voltage, type of voltage (i.e., AC,
DC, or pulsed DC), water temperature, and water
conductivity. Given these differences, it is not sur-
prising that investigators have reported different
results for the effects of e]ectrofishing, even for the
same species, For example, Kynard and Lonsdale
(1975), working with yearling rainbow trout, re-
ported 2% mortality among shocked fish, Hauck
(1949) reported a 26% monality of rainbow trout.
Lamarque (1967) found up to 93% mortality for
trout (species unknown) that he exposed to elec-
tricity. The last study demonstrates the enormous
variability in results; Lamarque (1967) found mor-
tality rates ranging from 0 to 93% depending on
the fish-to-electrode distance and the type of elec-
trical current used. These examples typify the dif-
ficulty in making generalizations regarding the ef-
fects of electricity on fish survival.
Our study differed from most others in that it
dealt with nongame fishes. All species examined
showed similar responses to electrofishing, al-

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